Variable resistance device



May 31, 1960 E. FALCO 2,939,097

' VARIABLE RESISTANCE DEVICE Filed March 11, 1959 Fig. 7 Fig 2 11 1 Fig. 3

United States Patent 2,939,097 VARIABLE RESISTANCE DEVICE Eugene Falco, 25, via Rossini, Turin, Italy Filed Mar. 11, 1959, Ser. No. 798,724 Claims priority, application France July 22, 1958 3 Claims. (Cl. 338-450) This invention relates to improvements in variable resistance devices, more particularly for use in electronics, the television or wireless telegraphy field.

In the above fields variable resistors are known which are more particularly used in potentiometers. Said resistors mostly comprise a graphite base material mounted on a support and connected with two terminals, a slider being movable between the terminals. It is more particularly advantageous to employ in the circuits adjustable resistors on account of the growing importance of transistors, which admit of fairly wide allowances.

Various devices are known in which the resistor is rectilinear, the slide moving in this case along a straight line; alternatively, the resistor is curved, the slider moving along a circumference.

The above known devices suffer from the main drawback that a relatively large number of components have to be assembled, among which'the movable slider is relatively delicate and uneasily accessible.

The devices=comprising rectilinear resistors are relatively tough, but the slider, which is connected with a lead, carries along the latter on displacement, which is apt to damage the lead and cause difliculties in assembly. V 7

Thecurve d resistor devices comprise a slider movable along a circumference connected to a stationary head portion arrange d at one end of the resistor. This a ran-gement avoids the. abovementioned drawback, but necessitates on the other'hand the provision of'a larger number of..components.

The improvements according to this invention fully remove all the abovementioneddrawbacks.

The resistor comprises a rotatable disc carrying on its surface a conductive material and a material of higher resistivity than the former, respectively, said. materials contactingieach other along a disc .radius and being separated'b'yaslit extending along another discgadius. Contact strips'ar'e" arranged to be in sliding contact with the conductive material and the less conductive material, respectively, rotation of the disc interposing between said contact strips a greater or smaller length of the less conductive material to thereby increase or reduce resistance.

The disc is serrated at its periphery for easily rotating it by one finger.

According to a characteristic feature of this invention a variable resistor, such as defined above, can be utilized in a potentiometer. For this purpose the two contact z a greater or smaller length of material of higher resistivity between the third strip and either current feed strip.

The device according to this invention provides a rotatable resistor instead of a rotatable slider, whereby a much smaller number of movable parts are required, which is of considerable advantage on assembly.

The accompanying drawings show two embodiments by way of example and not of limitation of devices provided with the instant improvements.

Figure 1 is a plan view of a variable resistance device,

Figure 2 is a side view of Figure 1,

Figures 3 and 4 are part sectional views on lines III-HI and IVIV of Figure 1, respectively and Figure 5 is a plan view of a rotatable resistor potentiometer.

Figures 1-4 show a support 1 in the form of a plate of relatively rigid insulating material, having mounted thereon a disc 2 fitted by a central aperture on a hub 3 on the support. Thehub acts as a shaft for the rotatable disc 2. More particularly, the hub can be formed by part-punching of a support 1 of cardboard impreg-.

nated with the material known by the trade name Bakelite (Figure 3). The surface of thedisc 2 is made at 4 of a material of higher resistivity and at 5 of a material of lower resistivity, such as a silver layer, the two materials contacting each other at 6 along adisc radius and being separated at 7 by a slit extending along a further diametrically opposed radius.

The disc is formed with a circumferential serration 8 through which its rotation can easily be controlled Two contact strips 9, 10, secured by;

by one finger. means of clips 11, 12 to the support 1, hear at two approximately diametrically opposed regions on the disc. The strips 9, 10, are each formed with an impression 90, 10a, respectively, extending towards the disc 2' and acting as a sliding contact. This impression holds its respective strip in parallel spaced relationship to the disc 2, whereby an electric contact between the strip and disc is established through this impression only.

On rotation of the disc ,a greater or smaller length of the material 4 of higher resistivity is interposed between the strips 9, 10, in orderto increase or decrease resistance. Stops can be provided" on .the support in order to limit the disc rotation, the said-stops coming into contact with steps 13, 14 provided at the disc periphery. The stops can easily be obtained by part-punching of the support 1. As will be seen from Figures 1 and 4, two arcuated tongues 30, ,31. obtained by part-punching are formed along an arcuated region adjacent part of the circumference of. the disc. 2, the tongue ends extending strips through which voltage reaches the device, are

sliding contact therewith.

In the abovementioned use in connection with a potentiometer, rotation of the disc results in interposition of beyond the face of'the support 1 carrying the disc 2.-

The tongues each form" an abutment surface 30a, 31a, respectively, which is abutted by its respective step, 14, 13, respectively, on the disc 2.

In the embodiment shown the angular width of the serrated region 8 on the disc and of the tongues 30, 31 are designed to afford a rotation of the disc through 180, namely to the left and 90 to the right of the middle position shown. On rotation of the disc, such as in clockwise direction from the position shown, the effective length of the resistive layer 4 is increased on the path between the sliding contacts 9a, 10a. More- Over, in the embodiment shown this path extends over an are A smaller than so that, in one of the end positions of the disc, both sliding contacts 9a, 10a are situated on the resistive layer 4, while in the opposite end position of the disc both contacts are situated on the conductive layer 5. In the first mentioned end position the resistance of the path is highest, while it is lowest or even nil in the second mentioned position.

From a mechanical standpoint it should be noted that the disc 2 is pressed against the support 1 by the pressure of the strips 9, 10, only. Manufacture and assembly of the device are thereby considerably simplified.

Figure 5 shows a potentiometer. As distinct from the embodiment shown in Figures l-4, in which the slit 7 in the disc 2 extends in a radial direction, the slit in the disc 102 shown in Figure 5 is of a complex form comprising two substantially radial portions 1070:, 107b, approximately diametrically opposite each other, merging into each other by an arcuated portion 107c concentrical with the disc. The structure of the disc 102 there fore includes two concentrical arcs, namely an outer arc sector 105 and an inner arc sector 105a, which angularly extend in opposite directions from a sector104 the angular width of. which but slightly exceeds 180". The arcs 105, 105a are covered with a material of low resistivity, the sector 104 being covered with a material of high resistivity.

The strips 109, 110 are connected with the current inlet leads, the voltage difierence being applied between the said strips.

On rotation of the disc 102 which can be moved by one finger acting on the serrations 108, the sliding contact 109a on the strip 109 remains in contact with the are 105, the contact 110a on the strip 110 contacting the arc 105a, whereby current flows through the material 104 of higher resistivity. A strip 122 is so arranged that in the various possible positions of the disc 102 the sliding contact 122a is in contact with the material 104 for the purpose of interposing a greater or smaller width of resistive material between itself and each of the strips 109 and 110.

In Figure 5 the disc is shown in one of its end positions, in which the sliding contact 122a on the strip 122 is in proximity to the arc 105a of lower resistivity. The disc 102 is capable of rotation from this position in anticlockwise direction only.

Stops 130, 131 can be arranged on the supporting plate 101 in order to stop the disc 102 in its extreme angular positions.

In the opposite end position of the disc, when the latter is rotated approximately through 180 away from the position shown, the strip 109 is still in contact with the are 105 at the free end region 'of the latter. The strip 110 still contacts the arc 105a at the root section of the latter, the strip 122 being in contact with the material 104 in proximity to the root section of the are 105. In this case the resistance interposed between the strips 120, 109 is lowest.

Similarly to the embodiment shown in Figures 1-4- the disc 102 is mounted on its support 101 having a hub 103 which acts as a shaft on which the disc 102 rotates.

It will be understood that this invention is not limited to the constructional embodiments described above and includes any modification thereof,

The invention further covers any embodiment having a resistor comprising a movable member having two arms sliding beneath two current feed strips, the displacement of the movable element in either direction increasing or decreasing the length of the electrical resistant path between the said strips.

What I claim is:

1. A potentiometer device comprising a supporting plate of an electrically insulating material, a boss protruding from one planar face of the plate, a disc rotatable on the boss, said disc including a sector-shaped section having a resistive exposed surface, and a pair of oppositely extending concentrical arc sections having conductive exposed surfaces, and three metal strips fixed on the supporting plate having each a free end section pressing the disc against the said planar face, the freed end sections of two of the said strips abutting on the arc sections of the disc, respectively, in a sliding contact therewith, and the free end section of the third strip abutting on the sector-shaped section of the disc, whereby a more and less resistive path is interposed between the third strip and the said two of the said strips, respectively, on angularly displacing the disc on the boss.

2. A variable resistance device comprising a supporting plate of an electrically insulating material, a pair of metal strips fixed on the plate in a mutually spaced electrically insulated relationship, said strips having each a free end section extending over one face of the plate, a boss on the said face of the plate at a location intermediate the free end sections of the strips, a disc-shaped resistor member rotatable on the boss, the said resistor member being applied against the said face by the said free end sections of the strips and having its strip-engaging surface including more and less resistive areas thereby providing a current path between the strips the resistance of which is a function of the angular position of the resistor member on the boss, and cooperating stop means fast with the resistor member and plate, respectively, defining angular end positions of the member relative to the highest and lowest resistance values, respectively, of the current path.

3. In the device as claimed in claim 2, the said stop means comprising a pair of radial steps angularly spaced on the circumference of'the resistor member, and a pair of tongues part-punched in the plate having their tip sections protruding on the path of the respective steps on the member to thereby stop the member in angularly different end positions.

References Cited in the file of this patent UNITED STATES PATENTS 2,172,634 Axtell Sept. 12, 1939 2,777,039 Thias Jan. 8, 1957 2,798,137 Rasmussen July 2, 1957 

